The present invention relates generally to the field of disc drive data storage devices, and more particularly but not by way of limitation, to an inertial spring latch assembly and compressive limit stop for limiting the movement of an actuator while dissipating energy from contact of the actuator with the inertial latch in a disc drive.
Hard disc drives are used in modern computer systems to enable users to store and retrieve vast amounts of data in a fast and efficient manner. A typical disc drive is generally composed of a head/disc assembly (HDA) which houses requisite mechanical portions of the drive and a printed wiring assembly (PWA) which supports requisite electronic portions of the drive.
The HDA includes a base deck to which various components are mounted and a top cover which cooperates with the base deck to form a sealed housing to reduce particulate contamination. Within the housing, a disc stack is formed from one or more magnetic recording discs which are axially aligned for rotation by a spindle motor at a constant, high speed, such as 10,000 revolutions per minute during normal disc drive operation.
A rotary actuator assembly is mounted adjacent the disc stack and includes a plurality of rigid arms which extend into the stack between adjacent discs, as well as above and below the top and bottom discs. The rigid arms support flexible suspension assemblies which in turn, support a corresponding number of read/write heads adjacent the surfaces of the discs.
Each of the read/write heads is mounted to the rotary actuator arm and is selectively positioned by the actuator arm over a pre-selected data track of the disc to either read data from or write data to the data track. The read/write heads each include a slider assembly having an air bearing surface that, in response to air currents caused by rotation of the disc, causes the heads to fly adjacent to the disc surface with a desired gap separating the read/write head and the corresponding disc. Each head typically includes a thin-film inductive write element to write data and a magneto-resistive (MR) read element to read previously written data. The write element generally comprises a ferromagnetic core about which a conductor is wrapped multiple times to form a coil.
When the disc drive is not in use, each read/write head is brought to rest upon the adjacent disc in a parking zone where data are not stored. Typically, each read/write head is positioned adjacent the parking zone before the rotational velocity of the spinning discs decreases below a threshold velocity. Below this threshold velocity, the spinning discs are unable to sustain an air bearing sufficient to support of the read/write heads. The parking zone is typically located near the inner diameter of the discs.
Once the heads are positioned in the parking zone, it is necessary to secure the actuator assembly by a latching arrangement to prevent the read/write heads from subsequently moving out onto the data storage zone of the discs while the disc drive is non-operational. Latching arrangements are generally practiced in the art and have included various configurations of springs, solenoids and magnets to secure and release the actuator. For example, see U.S. Pat. No. 5,187,627 issued Feb. 16, 1993, to Hickox et al; U.S. Pat. No. 5,224,000 issued Jun. 29, 1993, to Casey et al; and U.S. Pat. No. 5,231,556 issued Jul. 27, 1993, to Blanks.
While operable, such prior art latching systems suffer from several limitations. Mechanical latches typically are complex while electromechanical latches require substantial electrical power to operate. Many magnetic latches with open magnetic circuits exert considerable force when the actuator is near the latch, yet still over data tracks, thus resulting in increased power consumption. Moreover, such force can limit the maximum holding force generated by the latch.
Still other prior art latches such as inertial latching mechanisms can be ineffective upon application of a mechanical shock to the system. In particular, the contact surfaces of the latch mechanism and the moving portion of the actuator are encouraged in opposing directions in response to applied mechanical shocks. Therefore, the accelerations imparted to the latching mechanism and to the moving portion of the actuator can cause the contact surfaces to meet with a greater degree of force, resulting in xe2x80x9cbouncexe2x80x9d at the contact surfaces which tends to overcome the latching mechanism and thereby disengage the latching mechanism.
In conjunction with providing effective latching of the actuator as the disc drive comes into the non-operational mode, it is necessary to limit the actuator movement to prevent actuator arm/gimbal assembly and disc contact since faster seek times demand increased velocity of the actuator assembly. It is necessary to precisely control the extent of actuator travel relative to the non-data zones; otherwise, an actuator that travels beyond the desired extent of radial travel likely results in damage to the read/write head. The inner extent of radial travel allows the read/write head to travel inwardly past the inner most data track to the landing zone where the read/write head can be parked on the disc surface when the disc drive is inoperable. Inward travel beyond this inner extent of travel can result in damaging contact of the read/write head with the spindle motor hub. The outer extent of radial travel allows the read/write head to access the outer most data track. Outward travel beyond this outer extent of travel can result in the read/write head moving beyond the outer edge of the data disc where there is no sustaining airflow, causing damage to the read/write heads which can contact one another or the spinning discs.
As requirements for faster data processing demand ever increasing actuator speed and associated deceleration rates during seek cycles, the likelihood of overshooting the target track increases. Such an overshoot near the extents of travel can resultingly damage the read/write heads. Also, control circuit errors are known to create xe2x80x9crunawayxe2x80x9d conditions of the actuator wherein the actuator fails to decelerate at the appointed time. To protect the read/write heads from catastrophic failure, it is well known and practiced in the art to employ positive stops which limit the actuator travel to locations only between the desired extents of travel.
In providing such a positive stop, or limit stop, it is necessary that the limit stop decelerate the actuator quickly and in a short distance, but without damaging the actuator assembly. Applying a general dampened braking impulse is known in the art, such as by the use of an air cylinder type dampener as taught by U.S. Pat. No. 4,937,692 issued to Okutsu. In this approach fluid is displaced by a piston that is responsive to a stop member that obstructs the movement of the actuator beyond the desired extent of travel. The dampened braking impulse provides a resistive force for decelerating the actuator, but without the typical sudden deceleration of a rigid stop member, such as a rigid stop pin.
Manufacturability and cost constraints have urged the art toward more simple mechanisms. The use of a resilient pad is widely known, such as that of the teaching of U.S. Pat. No. 4,890,176 issued to Casey et al. and assigned to the assignee of the present invention. Spring members, too, are widely used in the art, such as that according to the teaching of U.S. Pat. No. 4,635,151 issued to Hazebrouck. The primary objection to resilient pads and springs, however, is the relatively long stopping distances necessary to compress the responsive member sufficiently so as to develop an effective braking force.
One attempted solution is to provide a preload force to the resilient member, such as is taught by U.S. Pat. No. 4,949,206 issued to Phillips et al. Another approach is to provide cantilever members that elastically deflect in response to the impact force of the actuator, such as is taught by U.S. Pat. No. 5,134,608 issued to Strickler and U.S. Pat. No. 5,600,516 issued to Phillips et al. and assigned to the assignee of the present invention. Where the resilient member provides a superior initial impact response in not significantly increasing the peak deceleration rate, the relatively large amount of disc space necessarily reserved for stopping distance runs counter to the efforts in maximizing disc space utilization.
Consequently, there has not been available a latching device nor a limit stop which will universally meet the ever increasing demands of disc latching and actuator movement control in reducing the susceptibility of damage to the disc drive. It is to such ends that the present invention is directed.
The present invention relates to a disc drive having an improved inertial spring latch assembly and compressive limit stop.
As exemplified by preferred embodiments, an inertial spring latch assembly is provided for latching an actuator in a disc drive. The actuator has a coil immersed in a magnetic field established by a magnetic circuit of a voice coil motor. The inertial spring latch assembly has a latch body pivotable about a pivot axis between a latched position and an unlatched position and disposed in a gap between an upper magnet and a lower magnet. A forward arm extends from the latch body in a first direction away from the pivot axis and comprises a first ferromagnetic member which interacts with the magnetic circuit to initially attract the latch body to the latched position. A trailing arm extends from the latch body in a second direction away from the pivot axis, so that the forward arm and the trailing arm extend on opposite sides of the pivot axis. The trailing arm comprises a second and third ferromagnetic member which interact with the magnetic circuit to secure the latch body in the latched position.
A spring member extends from the latch body and comprises an actuator contact surface so that the spring member deflects to reduce the contact forces of the actuator when the actuator is brought to a latched position. In particular, the actuator contact surface of the spring member comprises a spring arm and a contact post extending therefrom to provide a low stiffness contact surface when the actuator is brought to a latched position so that the spring arm and the contact post both deflect to provide a dual spring effect.
A compressive limit stop for supporting a magnetic circuit on a base deck of a disc drive is provided. Furthermore, the compressive limit stop limits travel of the actuator pivotally supported for movement of a read/write head over a rotating disc. The compressive limit stop comprises of a rigid body disposed within the base deck which supports a top pole and a bottom pole of a magnetic circuit on the base deck. A compressive sleeve is disposed about the rigid body and deflects upon impact of the actuator so that the compressive sleeve and the rigid body act in conjunction to decelerate and thereby limit the travel of an actuator.
The advantages and features of the present invention will be apparent from the following description when read in conjunction with the drawings and appended claims.